When supplying a Light Emitting Diode (LED), the current flowing through the LED is typically regulated at a predetermined value. Thus the power source for supplying a LED can be deemed as a current source. FIG. 1 illustrates a schematic diagram of a prior art LED power supply system 100. The power supply system 100 adopts a converter 12 to convert an Alternating Current (AC) power source 11, e.g. a 220 Volts, 50 Hertz commercial power, into a power supply with predetermined current for supplying a LED string 13. In practice, the current source I1 usually contains relative large current ripple which may lower down the life of LED string 13. In order to suppress the current ripple, a large output capacitor 14 is usually adopted. However, large output capacitor 14 may greatly increase the size and cost of system 100.
Accordingly, an improved method is desired to overcome one or some of the above mentioned deficiencies.